It is common to have a wireless mobile station to roam from one wireless network to another wireless network of a different wireless technology. For example, a mobile station often roams from a third generation (3G) network such as a Universal Mobile Telecommunication System (UMTS) network to a second generation (2G) network or vice versa. Part of the handover of the mobile station from one network to a target network is to ensure the security of the signaling and data when they reach the target network, in particular when the target network is a UMTS network. The security is achieved by the exchange of the security parameters between the network and the mobile station needed for ciphering and integrity protection of signaling and data radio bearer in a connected mode.
An inter-radio access technology (RAT) handover information includes a start packet switched (START PS) value, an UMTS security parameter associated with the mobile station that is used in the UMTS networks in packet switched domain. Different networks may have different methods of obtaining the inter-RAT handover information including the START PS value. For example, a long-term evolution (LTE) network node may obtain the START PS value by querying the mobile station for the inter-RAT handover information including the START PS value when the mobile station roams into the LTE network, which is generated by the mobile station. On the other hand, a 2G network node such as a Global System for Mobile communications (GSM) network node may pass a received inter-RAT handover information including the START PS value to a next GSM network node.